For a long time, adhesive restorations of the lateral tooth in the form of an amalgam1 have played an important role in the field of restorative therapy and are usually used these days without any additional underfilling. Only in the case of indirect restoration such as ceramic inlays and ceramic crowns, a reconstructive underfilling is still considered to be a meaningful process. However, this reconstructive underfilling can also consist of an adhesively attached stump construction composite.
The function of the underfilling—protecting the tooth from chemical, thermal and mechanical noxa—is taken over by dentin adhesion; provided that it is used correctly, because only then can it avoid a post-operative disorder on the one hand and can provide a bacteria-proof sealing to the dentin: The bacterial penetration alongside open dentin tubules is one of the main reasons for applying a filling. In the most disadvantageous case, bacteria or toxins can penetrate into the pulp via the dentin tubules and cause a case of pulpitis or an infected necrosis. However this can be avoided by sealing the surface sufficiently with a dentin adhesive as effectively as by using an underfilling. Then the metal-free reconstruction made of composite or ceramics also takes care of the thermal and mechanical protection of the dentin wound.
The following is an argument that is difficult to invalidate for the use of separate underfillings: If a composite filling would have to be removed again, it is a laborious procedure for the therapist to remove tooth-colored composite from deep areas near the pulp or at the cervical cavity border completely [2]2. Often more tooth substance is removed than necessary [3, 4, 5]3 4 5, and often this results in an iatrogenic exposure of the pulp. In addition, Krejci specifies the increased time factor in the composite revision with an average revision time of 24 minutes compared to, for example, 11 minutes with glass isonomer cement and 15 minutes with amalgam fillings [2]. Other authors state shorter revision times in composite restorations [6]6, but also describe a relatively longer treatment time as regards other materials that are not tooth-colored.
In general and according to manufacturer's instructions, a composite filling should not have to be removed again at all since it promises lifelong durability. However the clinical reality shows a different picture: here, a composite restoration has to be removed every now and then even though composite materials can be repaired by all means. As to the possibility of repairs, adhesive composite restorations are clearly superior to other restoration materials. However, there are individual indications that call for a complete removal of the entire composite material from the cavity. It is not possible for the therapist to simply move into the cavity along its brown edge. Besides, there is always the risk of causing injury to the pulp in deep areas near the pulp. Often, for reasons of “safety” more tooth substance is removed than is actually necessary: Millar et al. describe that in the revision of composite fillings, the cavities iatrogenically increase up to 37% [6].
There have been experiments already to cope with this problem by marking the dental materials with a photochromic dye (DE19520016C2). The photochromic dye contained in the dental materials changes color for a short period of time to olive-brown when exposed to a polymerization lamp, and the therapist can then discern whether he is still working in the area of the filling. The development led to the product “Tetric® Flow Chroma” of the company Vivadent, Liechtenstein. Szep et al. [5] examined the application of Tetric Flow Chroma in an in vitro-study. Surprisingly they found a significant reduction of the loss of tooth substance during the revision of the fillings only when Tetric Flow Chroma was applied also on the cavity walls and not exclusively on the cavity floor. Also no significant reduction of the revision time could be determined during the use of Tetric Flow Chroma exclusively on the cavity floor, or even during the use of the material on all cavity borders. This may be partly due to the necessary additional light activation of the photochromic substances with the polymerization lamp. The light exposure had to take place several times, the color change did not remain for an excessively long period of time and could additionally be activated by a thinner filling during the normal routine checkup of restorations. This, in turn, gave the therapist an “unpleasant feeling,” if a brown shimmer were noticeable below the restorations. Since of course the therapist always has to remove restorations of another person, but never his own, the question that remains unanswered here is whether this brown shimmer is a caries existing below the filling or whether it is the application of Tetric Flow Chroma. There is also the requirement for suitable underfilling materials that do not cause any baseless suspicion of caries.
In addition, adhesives with properties of color change under the effect of light are suggested (U.S. Pat. No. 6,528,555 B1), wherein the color change is permanent. Dental materials with reversible color change have also been described in U.S. Pat. No. 6,670,436 B2.
The task underlying the invention is to make available a flowable, light-curing underfilling material for composite fillings that is clearly visible after curing during or following the removal of a composite filling lying on it. This underfilling is distinguishable from the tooth substance without further measures such as additional lighting.
It is necessary to find a compromise between the goals of achieving full opacity, white color and complete curing of more than 1 mm (determined as per ISO-norm 4049) in light polymerization. This 1 mm originates from the specification of ISO norm 4049 for opaque filling materials.
It is important to implement a high opacity of the bright white colored flow composite, since such a material is used only in a thin layer. If a demarcation material of this type had the same opacity as a conventional flow composite, it would not be discernable on the tooth substance despite its white color. The setting of an appropriate high opacity is technically no problem, as opposed to the subsequent light-curing of the material. The more opaque a light-curing material is, the fewer layer thicknesses can be polymerized in a polymerization cycle.